"how long does it take to ferment or dry out when layed out on the garden soil? "

Depend's humidity,rain,sun,temperature and other things. It doesn't matter anyhow. Mix with compost,leaves or other carbons when you put it out. Laying on top will alow N to escape to air. Mixing with carbons will supply N to compost carbons. Personally,I prefer doing it in a bin or heap then tilling in while prepping ground in spring.

I agree with Klem. Do not put it on or in the soil. There are too many variables and once it's in you can't take it out.

You want it to compst with other materials. That can either be done in a compost pile or in a mulch mix on top of the beds. Mix with chopped leaves or straw, add moisture, and let nature take its course. The whole mixture will be safe for soil by the time summer vegetables go into the ground.

I would either till it in or put something on top such as relatively high carbon compostables. Fall leaves would be good. Many people put fresh manure on in the fall, it's decomposed and pathogens are gone by spring. But I agree putting it on the surface will result in lost N.